As used herein, the term “agroproduct” is defined to include anything that may be physically applied to a farmer's field. This may include, by way of example, fertilizers, pesticides, manure, any type of soil amendment, nutrients, water, polymers, compost, soil fumigants, pH adjusters, and seeds. Purchasing and applying these agroproducts is one of the major expenses of modern farming.
Farmers traditionally apply agroproducts at blanket application rates. Recent advances in precision agriculture technologies recognize that the application of agroproducts should not be done so blindly. For example, the addition of chemicals to soil may be overdone as well as underdone where the application of one material to the soil may cause an imbalance in other materials, such that curing one deficiency causes a problem in another soil property. This is shown where adding some lime to soil may raise an acidic soil's pH to an optimum range for a given crop and increase crop yields, but adding too much lime can raise the pH beyond the optimum range and result in decreased yield. Similarly, while application of key nutrients like fixed nitrogen and phosphate to soil deficient in those nutrients often increases crop yield, application of excessive amounts of those nutrients is wasteful and expensive. The excess nutrients may leach out of the soil to cause pollution issues in creeks, rivers, and lakes downstream. It is therefore desirable to avoid blanket application of chemicals by applying only a necessary amount of each chemical to the soil. Variable rate application of agroproducts may optimize crop yields while minimizing the use of agroproducts.
In order to determine a necessary amount of each agroproduct to apply to soil, farmers may pull soil samples for analysis on commercial order. A laboratory may quantitatively analyze the soil samples to determine existing soil nutrient content, pH, and other conditions. The soil nutrient content, pH, and conditions are compared to optima for a crop grown in the field. This information is used to determine an appropriate combination of agroproducts to be applied. Sampling need not be limited to soil samples, where other sampling techniques include, for example, plant tissue samples or insect counts to facilitate the informed delivery of agroproducts.
Modern farms may be quite large. An individual field is often a mile or more across. As such, soil nutrient content, pH, available water, and other conditions may vary significantly from one part of the field to another. These variations may result from differences in underlying strata intersecting the surface, from areas subjected to flooding from nearby streams and rivers now or in the past, from differences in elevation that cause water to flow preferentially to some portions and away from others, from variations in chemical application history between portions formerly owned by different owners, from differences in runoff received from neighboring fields, and for many other reasons.
Plants do not care about history, legal property lines or field boundaries. Each crop plant in a field is sensitive to nutrients, pH, and other attributes of its own root zone—not to conditions hundreds of feet or a mile away whether or not in the same field. Given the size of modern fields, it is desirable to map soil nutrients, pH, and other conditions across the field, and to vary the mix and quantity of chemicals applied to different portions of the field according to the nutrients, pH, and other conditions present in each portion of the field.
There is a cost, however, associated with sampling and associated analysis. By way of example, it is typically not practical to perform enough chemical analyses of enough samples to directly map nutrient content, and pH, across an entire large, modern, farmer's field, especially when the properties under study may change from year to year. For these reasons it is problematic in the art that variable application rates are, practically speaking, too often indeterminable.